In recent years, mobile wireless communications have become increasingly popular. Initial implementations of mobile wireless communications, for example in the form of cellular telephone networks, supported circuit switched voice communication services. Today wireless carriers also offer packet data communication services to their mobile customers. A significant advantage of wireless communications is mobility, that is to say, the ability to communicate at virtually any location throughout a wide geographic area and/or while moving or roaming about that area. At the same time, the mobile communication devices, typically handsets or personal digital assistants (PDAs) or the like have become quite small, light and portable. As a result, subscribers to mobile wireless communication services routinely carry their mobile devices with them wherever they go and as they travel, including when they travel on commercial transport vehicles like buses, trains and airplanes.
Traditionally, the use of mobile communication devices on commercial transport vehicles has been limited or prohibited entirely. For example, on airplanes, in-flight use of such devices is prohibited, as the high power levels required to communicate with ground-based cell sites might interfere with aircraft navigational communications or other operations of the airplane.
Small-scale cellular wireless systems have been developed for indoor use, e.g. to provide wireless private branch exchange type services. US application publication no. 2003/0013489 to Mar et al., for example, discloses an IP-based technique for providing wireless communication services for an enterprise. Mobile devices communicate with pico cells when within the enterprise premises and with macro base stations of a public cellular network when outside the enterprise.
In general, a small scale or indoor cellular communication system may be referred to as a “pico cell” system, with the outdoor cellular communication system being referred to as a “macro-cell” system. Within such a system, each pico cell consists of a spectrally dynamic (frequency agile) base station provided within the aircraft. For example, the pico cell may include a scaled down cellular transceiver for GSM communication or a scaled down cellular transceiver for CDMA communication.
Recently, a number of parties involved in the wireless communication industry and/or the airline industry have proposed the use of pico cells to provide connectivity between a customer's handset and the pico cell within an airplane. U.S. Pat. No. 6,314,286 to Zicker, for example, proposes a miniature cellular network for use in an airplane, including internal base stations and an air-to ground communication link. The advantage of a pico cell type system in the vehicle is that customers can use their own mobile station equipment on the plane or other vehicle. Also, the mobile handsets or the like can be operated at very low power, reducing interference they might otherwise cause at ground base-stations and/or with aviations systems of the airplane.
In a typical system now being proposed for vehicle applications, there will be at least one GSM transceiver and at least one CDMA transceiver. The two transceivers may form two pico base stations or may be integrated into a single pico base station.
A problem with such a pico cell approach in airplanes is that the transmissions from the airborne system and the mobile devices in the airplane interfere with the reception of customers' handsets in use on the ground. For example, signals from airborne handsets would also be received at ground base-stations. Although the airborne handset operations are at reduced power levels, the path between the aircraft and ground base-stations is unobstructed. Theoretically, the aircraft could be redesigned to reduce leakage, e.g. by adding shielding to the aircraft windows and to the passenger compartment. However, any solution involving extensive modification of the aircraft would be expensive and difficult or impossible to adapt to aircraft that are already in service.
Similar interference problems with regard to public network base station communications may arise in other vehicle or indoor applications of pico cell systems. Hence, a need exists for a technique to minimize the impact of interference between wireless station communications with the pico cell system and external public wireless networks. For vehicle applications, such as in airplanes, the solution should not require extensive modification or upgrade to the vehicle.